1. Field of the Invention
The present invention relates to mycoherbicidal delivery compositions, their preparation and to biological methods for controlling aquatic weeds.
2. Brief Description of the Prior Art
Infestations of aquatic weeds such as hydrilla result in an array of ecosystem disruptions by preventing sunlight from reaching other plants and animals. The plants can multiply in such numbers that they choke lakes and rivers, causing eutrophication. The vegetative mat can interfere with navigation, disrupt the functioning of drainage, irrigation, flood control and water conservation projects, block the withdrawal of water to hydroelectric and water plants, provide breeding grounds for disease carrying mosquitoes and snails, and reduce the fish population.
The most common methods for controlling the growth of nuisance aquatic weeds have been mechanical and chemical. A more environmentally friendly and cost-effective technique would make use of biological agents such as mycoherbicides.
Prior art formulations for controlling aquatic weeds such as hydrilla with Mycoleptodiscus terrestris have included product forms such as fermentation slurries, emulsifiable oils, syrups, cellulose, gums and alginates. For ease of application, granules or pellets are preferred. Prior art formulations of M. terrestris offer non-targeted control of aquatic weeds and other pests since the particle sizes, densities and intrinsic coacervating gelling properties of the formulations make the particles fall off the targeted surfaces. Previous formulations tend to dilute themselves in water or sink to the bottom thus diluting the biological control agent and missing the target plant. The formulations require higher application rates than would be required if the material could be applied in a more targeted fashion. In prior art granule and pellet formulations, the viability of the fungus is reduced, particularly when the fungus is present as mycelium.
Prior art formulations with wheat flour and other starches gel or agglutinize in the presence of moisture during processing in extruders, tablet presses and pelletizers and do not disperse well in water. Formulations with corn cob grit float and do not target submerged aquatic plants. Other nut shell grits such as almond and peanut hull grits similarly float and do not coat submerged aquatic plants.
Ideally, the viability of the fungus would be maintained and the granule or pellet would dissolve or break apart in such a manner that the fungus is suspended in the water near the weed in a form that it adheres to the plant, allowing sufficient contact time for infection. These objectives are critical to the practical success of a mycoherbicide for aquatic weeds, particularly those that are submerged, and have not been satisfied by prior art delivery compositions.